Last night we flew the spinnaker on Alien without a pole, using a
spinnaker-guy, which is much like the Tacker. This setup is for a beam reach
and not quite right for running dead downwind.
My question is on mainsail trim. Sailing with the mainsail trimmed "ideally"
seems to block the spinnaker to some degree. I've been told that overtrimming
the main a bit is best, but I see pics that dispute this.
Anyone have experience/ideas for this setup?
Obviously, rigging the pole is best, but it can be a drag when Suzanne and I
sail alone.

The sail in your pic looked more like a gennaker or some kind of reaching chute
than a spinnaker. The tacker, if I understand it correctly, replaces the pole
and attaches to the spin's tack and keeps it at the headstay. This is like
having the pole all the way forward, which would be appropriate if you were
sailing hotter (ie, higher). In that case, you want to trim the main and it
should not be blanketing the chute. You were probably just experiencing too
light winds and chop. Where is the guy led with that sort of contraption?